Immunopathologic patterns of cyclosporine deposition associated with nephrotoxicity in renal allograft biopsies

Using antibody directed against cyclosporine (CsA-Ab) in an avidin-biotin-complex immunoperoxidase technique on routine formalin-fixed tissue specimens, 46 renal biopsies from CsA-treated renal allograft recipients and 23 biopsies from non-CsA-treated patients were examined to identify staining patterns potentially associated with CsA nephrotoxicity (CsA-NT). All specimens were examined independently in a masked fashion by two pathologists for the intensity of (CsA-Ab) specific staining for each of the four distinct patterns identified: diffuse interstitial staining (DIS, 0–3+); fine granular staining of tubular epithelium (FGS, 0–3+); coarse granular staining of tubular epithelium (CGS, 0–3+); and dark cellular staining of mononuclear inflammatory cells (DCS, 0–3+). Based on standard clinical criteria all CsA-treated patients were categorized according to the degree of CsA nephrotoxicity (grades 1—4).